The VIRTIO_BALLOON_F_PAGE_POISON feature bit is used to indicate if the
guest is using page poisoning. Guest writes to the poison_val config
field to tell host about the page poisoning value in use.

Signed-off-by: Wei Wang <wei.w.w...@intel.com>
Suggested-by: Michael S. Tsirkin <m...@redhat.com>
Cc: Michael S. Tsirkin <m...@redhat.com>
Cc: Michal Hocko <mho...@suse.com>
Cc: Andrew Morton <a...@linux-foundation.org>
---
 drivers/virtio/virtio_balloon.c     | 13 +++++++++++++
 include/uapi/linux/virtio_balloon.h |  3 +++
 2 files changed, 16 insertions(+)

diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index 39ecce3..9fa7fcf 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -685,6 +685,7 @@ static struct file_system_type balloon_fs = {
 static int virtballoon_probe(struct virtio_device *vdev)
 {
        struct virtio_balloon *vb;
+       __u32 poison_val;
        int err;
 
        if (!vdev->config->get) {
@@ -728,6 +729,12 @@ static int virtballoon_probe(struct virtio_device *vdev)
                        goto out_del_vqs;
                }
                INIT_WORK(&vb->report_free_page_work, report_free_page_func);
+               if (virtio_has_feature(vdev, VIRTIO_BALLOON_F_PAGE_POISON)) {
+                       page_poison_val_get((u8 *)&poison_val);
+                       memset(&poison_val, poison_val, sizeof(poison_val));
+                       virtio_cwrite(vb->vdev, struct virtio_balloon_config,
+                                     poison_val, &poison_val);
+               }
        }
 
        vb->nb.notifier_call = virtballoon_oom_notify;
@@ -846,6 +853,11 @@ static int virtballoon_restore(struct virtio_device *vdev)
 
 static int virtballoon_validate(struct virtio_device *vdev)
 {
+       uint8_t unused;
+
+       if (!page_poison_val_get(&unused))
+               __virtio_clear_bit(vdev, VIRTIO_BALLOON_F_PAGE_POISON);
+
        __virtio_clear_bit(vdev, VIRTIO_F_IOMMU_PLATFORM);
        return 0;
 }
@@ -855,6 +867,7 @@ static unsigned int features[] = {
        VIRTIO_BALLOON_F_STATS_VQ,
        VIRTIO_BALLOON_F_DEFLATE_ON_OOM,
        VIRTIO_BALLOON_F_FREE_PAGE_HINT,
+       VIRTIO_BALLOON_F_PAGE_POISON,
 };
 
 static struct virtio_driver virtio_balloon_driver = {
diff --git a/include/uapi/linux/virtio_balloon.h 
b/include/uapi/linux/virtio_balloon.h
index 0c654db..3f97067 100644
--- a/include/uapi/linux/virtio_balloon.h
+++ b/include/uapi/linux/virtio_balloon.h
@@ -35,6 +35,7 @@
 #define VIRTIO_BALLOON_F_STATS_VQ      1 /* Memory Stats virtqueue */
 #define VIRTIO_BALLOON_F_DEFLATE_ON_OOM        2 /* Deflate balloon on OOM */
 #define VIRTIO_BALLOON_F_FREE_PAGE_HINT        3 /* VQ to report free pages */
+#define VIRTIO_BALLOON_F_PAGE_POISON   4 /* Guest is using page poisoning */
 
 /* Size of a PFN in the balloon interface. */
 #define VIRTIO_BALLOON_PFN_SHIFT 12
@@ -47,6 +48,8 @@ struct virtio_balloon_config {
        __u32 actual;
        /* Free page report command id, readonly by guest */
        __u32 free_page_report_cmd_id;
+       /* Stores PAGE_POISON if page poisoning is in use */
+       __u32 poison_val;
 };
 
 #define VIRTIO_BALLOON_S_SWAP_IN  0   /* Amount of memory swapped in */
-- 
2.7.4

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